FIGURE 4.

Analysis of inter-spin distances between nearest-neighbor spin labels in the transmembrane helix of TatA. In A, black line, 100% labeled Ile¹⁵ → Cys TatA. The protein concentration was 350 μm. Gray line, 10% labeled Ile¹⁵ → Cys TatA prepared by sub-stoichiometric addition of MTSL. The total protein concentration was 800 μm (gray line). The spectral intensities have been normalized to allow comparison of line shapes. Spectra were recorded under the following conditions: frequency = 9.65 GHz, power = 0.006 milliwatt, modulation amplitude = 1 gauss, temperature = 170 K. In B, black line, 100% labeled Ile¹⁵ → Cys TatA as in A. Gray line, simulation of the spectrum of 100% labeled Ile¹⁵ → Cys TatA using a fitting routine that takes account of dipolar broadening.